I just got the 6412 this weekend. I was unable to get any digital channels at all, just the regular analog channels. Made some calls to Comcast, they said things look good from their end, and offered to send a tech out. In the meantime, I tried a small signal amp and it allowed me to get some of the digitals, but with pixellation on some channels. Thinking the old, original cable in the walls wasn't helping anything, I pulled in new run of RG6 (fortunately, my nephew was over so I was able to enlist his help). Now, I'm getting all the channels I'm supposed to - however, when I swap tuners, I still have pixellation and the on-demand content is unwatchable on the second tuner.
It sure seems like this issue has something to do with signal strength, but it doesn't really make sense that it affects only one of the tuners. Does this sound like the same issue others are seeing in Delaware?